1. Field of the Invention
The present invention relates generally to an underwater branching device. More specifically, the invention relates to an underwater branching device for branching an optical submarine cable under the water.
2. Description of the Related Art
A conventional underwater branching device of this type is partially shown in FIG. 4. In FIG. 4, there is shown an optical submarine cable network in order to perform bidirectional optical communication between first to third stations (A to C stations) respectively located across an ocean. The A to C stations are mutually connected through submarine cables 1 to 3. These submarine cables 1 to 3 are branched for enabling mutual optical communication between respective of A to C stations within a underwater branching device 14 provided under the water.
In further detail, the submarine cable 1 has two pairs of optical fibers (hereinafter simply referred to as "fiber") 4-1, 4-2 and 5-1, 5-2. The submarine cable 2 has two pairs of fibers 4,1 4-2 and 6-1, 6-2. The submarine cable 3 has two pairs of fibers 5-1, 5-2 and 6-1 and 6-2.
A pair fibers 4-1 and 4-2 are employed for up-stream and down-stream communication between the A station and B station, a pair of fibers 5-1 and 5-2 are employed for up-stream and down-stream communication between the C station and the A station, and a pair of fibers 6-1 and 6-2 are employed for up-stream and down-stream communication between the B station and C station.
By the connection as illustrated in FIG. 4, optical communication between three stations, i.e. A to C stations located across the ocean can be performed.
The conventional underwater branching device has no measures for failure caused in the submarine cable or terminal system. The reason will be discussed with reference to FIG. 4.
When cut-off failure of the submarine cable is caused at a point a within the submarine cable, communication through the optical fibers 4-1, 4-2 and 5-1 and 5-2 is interfered. Therefore, the communication path becomes only optical fibers 6-1 and 6-2 connecting the B station and C station.
Similarly, when a failure is caused at a point b within the submarine cable, the communication path becomes only optical fibers 5-1 and 5-2 for only one system connecting the C station and A station. Also, when a failure is caused at a point c within the submarine cable, the communication path becomes only optical fibers 4-1 and 4-2 for only one system connecting the A station and B station. Therefore, in such case, the communication path cannot be used effectively.
If it can be realized in the underwater branching device 14 to connect the optical fiber 5-2 to the optical fiber 4-1 and the optical fiber 4-2 to the optical fiber 5-1, the submarine cables 2 and 3 other than the faulty submarine cable 1 can be effectively used so that one more system can be effectively used in the communication between the B station and C station.